V.E.R.A. -- Virtual Entity of Relevant Acronyms (February 2016):

PKI
       Public Key Infrastructure (cryptography, Internet, ITU, PKI)


The Free On-line Dictionary of Computing (30 December 2018):

Public Key Infrastructure
PKI

    (PKI) A system of public key
   encryption using digital certificates from Certificate
   Authorities and other registration authorities that verify
   and authenticate the validity of each party involved in an
   electronic transaction.

   PKIs are currently evolving and there is no single PKI nor
   even a single agreed-upon standard for setting up a PKI.
   However, nearly everyone agrees that reliable PKIs are
   necessary before electronic commerce can become widespread.

   US DOD PKI (http://www-pki.itsi.disa.mil/).

   US NIST PKI (http://csrc.ncsl.nist.gov/pki/).

   IETF PKIX Working Group (http://imc.org/ietf-pkix/).

   (1999-11-30)